If you think he's going to shoot you, you have nothing to lose by trying it. Glance past him, let your eyes widen just a touch and lift the eyebrows like you're trying to hide your surprise. Start to comply and then look past him again, opening your eyes wide in surprise. At the first sign of him moving, step to the side, draw and fire repeatedly.
If his weapon is well within your reach, you can avoid the theatrics and try slapping the gun aside as you step away drawing to fire.
Again, these are measures of last resort.
BillCA in CA (Unfortunately)